1. Field of the Invention
This invention relates to underwater life support apparatus and to personal direction indicators for environments lacking fixed visual reference objects.
2. Related Prior Art
When a diver tries to find his way underwater, a navigational device such as a compass is needed. Many of the present day diver's compasses attach to the wrist. With the wrist mounted compass, the diver must look toward his wrist in order to navigate. His body must usually be repositioned to allow for an accurate reading. It is difficult to focus his eyes on the indices of tee compass while his head and hands are moving in the water. Any movement of his eyes from the forward field of view to the compass on his wrist causes the diver to divert from his intended path. When traveling longer distances, the diver is required to look at his wrist many times, and the cumulative error resulting from these diversions is undesirable.
Prior art designs which attempt to solve this problem include the mask compass, described in U.S. Pat. No. 4,953,304 (Raitman) and U.S. Pat. No. 3,210,859 (Fisk). In these designs a compass mounted on a bracket assembly is moved from a stored position on top of the mask to a viewing position on the face of the mask. When needed, the diver rotates the compass into position. When in position, the compass blocks a fixed portion of the mask. Both designs require viewing optics to permit the diver to view the compass because without the lens or lens and prism in combination, the eye cannot recognize the close up markings. In addition, these monocular compasses substantially block the diver's vision out of one of his eyes. This is undesirable because a diver's total vision is required to prevent unnecessary collisions with underwater obstacles. These designs cover a fixed portion of the mask and therefore, create additional functional problems. If the mask should become dirty or foggy, at the section used by the compass, a diver cannot use the navigational device. The device :s also expensive because it requires a complex optical scope to view the compass. The design is further faulted because it requires a precise distance between the diver's eye and the lens for accurate viewing of the compass and therefore does not function equally well or requires adjustment for a variety of masks and face shapes. The diver also will suffer from unnecessary fatigue as only one eye can look into the optical lens.
In addition, the viewing window or eyepiece can become dirty or scratched making it difficult to reliably and clearly view the compass. Prior art design also fails to provide the diver with information providing his angle of ascent or descent. Also as the waters become dark, it becomes difficult to read the prior art compass because light from the water must reflect off the compass and pass through the optics before being viewed. This causes unnecessary attenuation of the limited available light.
Both prior art designs have operational problems as well. U.S. Pat. No. 4,593,304 (Raitman) uses a lens which focuses on a gimbaled compass. This design permits the compass to rotate so that the observer can obtain readings even when his head is not in the vertical position. However, in this mode the compass markings are out of focus because as the compass rotates, the distance between the flat compass rose and lens changes. The design does not compensate for these changes and the image is thus unclear.
Prior art Pat. No. 3,210,859 (Fisk) maintains a constant distance between the lens and compass. However, because the compass is not pivoted it will jam as the diver tilts his head.
U.S. Pat. No. 4,141,152 (White) also includes a lens compass combination. If this design was permitted to rotate the distance between the lens and eye would change and make it difficult for accurate viewing. None of the prior art designs use the refractive qualities of the water to enlarge the viewed symbols or marks of the compass rose.
Some prior art designs incorporate jeweled mechanical bearings to permit the compass to rotate and continue to function regardless of the diver's angular head position relative to the vertical. The friction in mechanical bearings inhibits the compass from attaining the exact horizontal orientation necessary for reliable readings.
Other designs not found in the patent literature include an orb shaped or ball compass mounted on the diver's wrist. All wrist mounted devices require the diver to frequently refocus and redirect his eyes from the forward direction to his wrist as he moves for directional guidance. However, the ball compass design is superior to the flat wrist mounted compasses in that it does not jam as the wrist is rotated in the vertical plane. Ball compasses include a single band of indices which align when the compass is held in the horizontal plane. Thus although the wrist mounted ball compass can rotate and does not jam as the diver ascends or descends it does not provide the additional reference markings required to identify angle of ascent or descent or the azimuth when in other than the horizontal position. A magnifying lens is not usable because the distance or the viewing angle between the diver's eye and ball compass varies.